The present invention relates to monolithic ceramic capacitors, and specifically to those having inner electrodes made of a base metal. Also, the present invention relates to a producing method of the monolithic ceramic capacitor.
Monolithic ceramic capacitors comprising conventional dielectric ceramic compositions that consist essentially of BaTiO3 were problematic in that the compositions are reduced into semiconductors if baked in neutral or reducing atmospheres having a low oxygen partial pressure. Therefore, it was necessary to use, as inner electrodes therein, noble metals, such as palladium, platinum and the like, that do not melt at temperatures at which such dielectric ceramic compositions are sintered, and that are not oxidized even when baked in atmospheres having a high oxygen partial pressure, so that such dielectric ceramic compositions can be baked without being converted into semiconductors. However, use of noble metals much interferes with the reduction in cost of the monolithic ceramic capacitors thus produced.
In order to solve the above-mentioned problems, it has been desired to use inexpensive base metals such as nickel as the material of inner electrodes. However, if such base metals are used as the material of inner electrodes and if they are baked under the conventional conditions, they are oxidized and lose their functions as electrodes. Therefore, in order to successfully use such base metals as inner electrodes, dielectric ceramic compositions having excellent dielectric characteristics are needed and which can be baked even in neutral or reducing atmospheres having a low oxygen partial pressure without making the layers of the compositions into semiconductors. As materials that meet such requirements, for example, proposed were compositions of the type of BaTiO3xe2x80x94CaZrO3xe2x80x94MnOxe2x80x94MgO, such as those disclosed in Japanese Patent Application Laid-Open No. 62-256422; compositions of the type of BaTiO3xe2x80x94MnOxe2x80x94MgO-rare earth oxide, such as those in Japanese Patent Application Laid-Open No. 63-103861; compositions of the type of BaTiO3xe2x80x94(Mg,Zn,Sr,Ca)Oxe2x80x94Li2Oxe2x80x94SiO2xe2x80x94MO (MO: BaO, SrO, CaO), such as those in Japanese Patent Publication No. 61-14610; and compositions of the type of (Ba,Ca,Sr,Mg,Ce)(Ti,Zr)O3, such as those in Japanese Patent Application Laid-Open No. 3-263708.
However, monolithic ceramic capacitors having inner electrodes of such a base metal were problematic in that if each dielectric ceramic layer is thinned while increasing the number of the layers laminated together, some residual stress is produced at the interface between the inner electrode and the dielectric ceramic layer due to differences in contraction and also in thermal expansion between the inner electrodes and the dielectric ceramic layers, thereby worsening the thermal impact resistance of the capacitors. As to reliability in high-temperature and high-humidity conditions, which indicates so-called wet load-resisting characteristics of the capacitors, the capacitors of that type were also problematic in that such their characteristics are worsened for the same reasons as above, if each dielectric ceramic layer is thinned while increasing the number of the layers laminated.
In order to solve these problems, Japanese Patent Publication No. 7-56850 discloses monolithic ceramic capacitors in which inner electrodes of Ni are bonded to the matrix body via an aluminosilicate layer. The aluminosilicate layer is a mixture of oxides of metals such as Ni, Si and Al which originate in the inner electrode paste. Further, firing is carried out under a non-oxidative condition, e.g. 1.5% of H2xe2x80x9498.5% of N2. However, the disclosed capacitors are still problematic in that their capacitance is low, that their equivalent series resistance is large, and that, if each dielectric ceramic layer is thinned, Al added to the inner electrode paste diffuses into such thin dielectric ceramic layers, thereby worsening the characteristics of the capacitors.
In addition, the thermal impact resistance of the capacitors is low.
On the other hand, Japanese Patent Application Laid-Open No. 3-133114 discloses monolithic ceramic chip capacitors in which oxide layers comprising components that are different from those constituting the dielectric layers are formed around the inner electrodes. In this, the samples are fired in atmospheres having a low oxygen concentration for the purpose of improving their reliability in high-temperature load tests. However, this baking method is ineffective in improving the thermal impact resistance and the wet load resistance of the capacitors.
In the ceramic chip capacitor, a manganese oxide layer is formed around an internal electrode. Oxides of Si/Ca/Ba/Ti/Zr/P which originate in the dielectric material may be included in the manganese oxide layer.
The object of the present invention is to improve the dielectric ceramic layers constituting a monolithic ceramic capacitor having inner electrodes of a base metal, thereby providing a monolithic ceramic capacitor having excellent thermal impact resistance and wet load resistance characteristics.
The present invention has been made in consideration of the above-mentioned object.
The present invention provides a monolithic ceramic capacitor composed of a plurality of dielectric ceramic layers, a plurality of inner electrodes formed between the dielectric ceramic layers in such a manner that one end of each inner electrode is exposed out of either end of the dielectric ceramic layers, and outer electrodes electrically connected with the exposed inner electrodes, which is characterized in that the inner electrodes each are made of a base metal and that Si oxide layers are formed adjacent to the inner electrodes.
The invention also provides a monolithic ceramic capacitor composed of a plurality of dielectric ceramic layers, a plurality of inner electrodes formed between the dielectric ceramic layers in such a manner that one end of each inner electrode is exposed out of either end of the dielectric ceramic layers, and outer electrodes electrically connected with the exposed inner electrodes, which is characterized in that the inner electrodes each are made of a base metal and that compound layers comprising an Si oxide and at least one component that constitutes said dielectric ceramic layers and said inner electrodes are formed adjacent to the inner electrodes.
In the monolithic ceramic capacitor of the invention, the base metal is preferably Ni or an Ni alloy.
In the monolithic ceramic capacitor of the invention, at least one component constituting the dielectric ceramic layers is preferably an Si oxide.